Annual forced expiratory manuevers were conducted over a 6-7 year follow-up period on 645 middle-aged participants in the Pittsburgh Center of the Multiple Risk Factor Intervention Trial (MRFIT). The Forced Expiratory Volume in One Second (FEV1), The Forced Vital Capacity (FVC), and the Forced Expiratory Flow Rates over 25-75% (FEF 25-75%) and 75-85% (FEF 75-85%) of the forced expiration have been measured and verified by two trained coders at the University of Pittsburgh during the first budget year. The expiratory tracings have also been rated for various aspects of the quality and acceptability of the tracings for use in the analysis. A preliminary analysis of the FEV1 slopes, by Smoking Status, was carried out for 293 subjects with at least 4 computerized, acceptable quality and reproducible FEV1s available for the analysis. The mean FEV1 slope for 14 smokers who quit smoking in year 0-1 of the Trial and remained ex-smokers for the duration of the Trial was -25 m1/yr, which was statistically significantly lower (p less than 0.01) than the mean slope for 93 subjects who smoked continually throughout the Trial, -64 m1/yr. This comparison will be refined in the final analysis to control for level of smoking and degree of airways obstruction. The distributions of FEV1 slopes tend to move in opposite directions for the continuing and recent ex-smokers: 17% of the continuous smokers exhibit slopes steeper than -100 m1/yr compared with 0% of the ex-smokers, and 29% of the ex-smokers exhibit positive FEV1 slopes over the Trial, compared with 6% of the continuous smokers. These preliminary findings are highly suggestive of a positive effect of recent smoking cessation on FEV1 deterioration over time. Given these findings, this competitive renewal grant application proposes to extend the Pittsburgh MRFIT analyses, which will be completed in 1984, to two other MRFIT centers with good quality pulmonary function testing conducted over the seven years of the Trial. The Principal Investigators from these other two centers have consented to have their smoking related data and pulmonary function tracings included in this extended analysis. Inclusion of these other two centers will permit an analysis of longitudinal pulmonary function changes in relation to smoking status in 1,950 MRFIT subjects, tripling the sample size available in the Pittsburgh center alone. This grant renewal will support the measurement and quality-review of approximately 7,200 spirograms from these two centers, and the analysis of the measurements in relation to the seven year Smoking Status.